1. Field of the Invention
The present invention relates to a linear motion rolling guide unit which is applied to sliding portions and rotating portions of machining tools, various precision machining equipments and testing equipments.
2. Description of the Prior Art
Conventional linear motion rolling guide units include a track rail formed with two or more raceway surfaces extending longitudinally on both side walls thereof; a slider having raceway surfaces facing those of the track rail and straddling the track rail; and a number of rolling elements that travel rolling between the facing raceway surfaces. In such rolling guide units, various kinds of retainers have been developed that support the rolling elements on a loaded area of the raceway surfaces. Many retainers consist of a flat plate member which is formed, when the rolling elements are balls, with a slit a slightly narrower than the ball diameter so that the balls can be supported by the slit.
The slider that slides on the track rail has a casing and end caps secured to the ends of the casing. It also has end seals attached to the ends of the end caps and an under seal attached to the underside of the slider. Further, the conventional linear motion rolling guide unit also has a number of rolls that travel rolling along the raceway formed between the raceway surface on the track rail and the raceway surface on the casing, and a retainer plate secured to the casing to hold the rolls in the casing.
Among such rolling guide units there is a four-raceway endless linear motion rolling guide unit. The four-raceway endless linear motion rolling guide unit will be explained by referring to FIG. 10, 11 and 12.
The four-raceway endless linear motion rolling guide unit has a track rail 1 almost I-shaped in cross section; a slider 2 mounted astride on the track rail 1 so that it is slidable on the rail; and a number of cylindrical rolls 3 rollably interpoped between the track rail 1 and the slider 2 so that the center axes of the adjacent rolls in the loaded area are parallel to each other. The track rail 1 is formed with recessed grooves 8 extending longitudinally on both side walls 18 thereof, the grooves 8 constituting the raceway surfaces 5, 6. Upper and lower edge portions of the grooves 8 of the track rail 1 are formed as inclined surfaces constituting an upper raceway surface 5 and a lower raceway surface 6. The slider 2 has a casing 4 which is formed with a recessed portion 10 so that the casing can straddle the track rail 1, and end caps 7 attached to both longitudinal ends of the casing 4. To seal the boundary between the track rail 1 and the slider 2 when the slider 2 slides on the track rail 1, the ends of the end caps 7 are each provided with an end seal 20 (FIG. 11) and the underside of the slider 2 with an under seal 22.
The recessed portion 10 of the casing 4 is formed with an upper raceway surface 11 and a lower raceway surface 12 at positions corresponding to the upper raceway surface 5 and the lower raceway surface 6 of the track rail 1. Between the upper raceway surface 11 and the lower raceway surface 12 of the casing 4 is formed an engagement groove 15, which engages with an engagement projection 16 formed on a retainer plate 9. The retainer plate 9 is loosely fitted in part in the recessed groove 8 of the track rail 1 and also fixed to the casing 4 by bolts 17.
In the above construction of the 4-raceway endless linear motion rolling guide unit, two raceways are formed on each side of the track rail 1 by the upper and lower raceway surfaces 5, 6 on the track rail 1 and the upper and lower raceway surfaces 11, 12 on the casing 4. Hence, a total of four raceways are formed on both sides of the track rail 1. In these loaded roller raceways, a number of cylindrical rolls 3 rotate in contact with the facing raceway surfaces 5 and 11 and with the facing raceway surfaces 6 and 12. The casing 4 is formed with return passages 13, 14, and the end caps 7 are formed with direction changing passages 32, 36 (FIG. 11) that connect the loaded roller raceways and the return passages 13, 14 . Hence, the loaded roller raceways, the direction changing passages 32, 36, and return passages 13, 14 form two endless circulating paths on one side. One of the endless circulating paths is, for example, disposed inside the other. That is, the two endless circulating paths have different lengths, with the shorter one placed inside the loop of the longer one in such attitudes that they cross but do not interfere with each other. The longer endless circulating path and the shorter endless circulating path have the same lengths of the loaded raceways. When the slider 2 slides on the track rail 1, a number of cylindrical rolls 3 circulate through the longer endless circulating path and another group of cylindrical rolls 3 circulate through the shorter endless circulating path. Though not shown, it is possible to form the two endless circulating paths in the same lengths by making them cross each other or to form them in upper and lower parallel paths.
Examples of such four-raceway endless linear motion rolling guide units include those of Japanese Patent Laid-Open Nos. 175564/1989 and Japanese Patent Application Nos. 106311/1990 and 166326/1991.
In the conventional four-raceway endless linear motion rolling guide unit, the mounting of the end caps 7 to the casing 4 requires precise positioning of the end caps 7 to correctly form two endless circulating paths with the loaded roller raceways, the direction changing passages 32, 36 and the return passages 13, 14 and thereby allow smooth rotating motion of the rolls 3 through the endless paths. It is also necessary to form an appropriate sliding surface at the boundary between the track rail 1 and the slider 2 to ensure a good seal.
When the retainer plate 9 is to be mounted to the casing 4, it is a common practice to pass the bolt 17 through a hole 23 in the casing 4 and screw it into a threaded hole in the retainer plate 9 to secure the retainer plate 9 to the casing 4. Further, the retainer plate 9 is required to have an engagement projection 16 that snugly fits in the engagement groove 15 formed in the casing 4. This in turn requires high machining precision not only for the retainer plate 9 but for the casing 4, raising the manufacturing cost.